The invention relates generally to sputtering targets and specifically to target cooling methods.
During sputtering, some cylindrical sputtering targets, also known as rotary cathodes, rely on coolant to remove excess heat. The heat input profile is determined by the shape and strength of the magnets combined with magnitude which is determined by the sputter energy provided by the sputter power supply.
Conventionally, coolant flow proceeds in an axial direction with water entering through one end of the target, and exiting at an opposite end. In U.S. Pat. No. 7,504,011 (Schmidt et al.), incorporated herein by reference in its entirety, coolant enters at a first end of the target, reverses direction near a second end, and exits again through the first end. Often, water serves as the coolant material to remove approximately 90-95% of the unwanted heat.
One problem associated with the conventional target configurations and methods for cooling targets is that water may stagnate due to tight clearances between the cathode magnets (also called a magnet assembly) and the inner diameter of the target backing tube. This reduces the heat transfer coefficient and may lead to non-uniform temperature distribution along the length of the target, with higher temperatures at the top than at the bottom, and generally higher than allowable temperatures on the target surface.